We propose to extend our work on the structure of wheat germ agglutinin (WGA) and to undertake studies of diphtheria toxin (DT), which has some functional similarity to WGA. The WGA structure has been determined to a resolution of 2.2 A by x-ray crystallographic methods and a sequence has been derived from this electron density map. The binding sites of the membrane components, sialic acid and oligo-N-acetylglucosamine, have been determined from difference Fouriers. In order to understand the nature of the binding of these molecules, we require a reliable sequence and the best quality electron-density map possible. Therefore, we propose to sequence peptides obtained by cleavage at cystine residues and to compare these with the tentative sequence from the electron-density map. Furthermore, we intend to refine the present electron-density map to obtain calculated phases for detailed analysis of the interactions with ligands and the inter-protomer interactions of WGA. To relate these structural data to the binding of WGA to cells, we propose to study the binding of complex carbohydrates to WGA. Diphtheria toxin is a bifunctional molecule which, in addition to its toxic activity, has a lectin like activity of specificity similar to that of WGA. We propose to study the binding, processing and transport of DT in HeLa cells. We will examine the specificity of oligosaccharide binding and compare it with that of WGA. We will also isolate the membrane receptor by electrophoresis and characterize it. By specific modifications we will test whether DT is capable of autoproteolytic activation and how disulfide reduction occurs during intoxication. These modified species will also be used to identify essential groups for the transport process. We will also characterize a copper-containing derivative of DT and examine its activity in vivo to determine the possible role of copper in any of the functions of DT and lectins.